Relative movement system having alarm means

ABSTRACT

A primary beam of light is directed on a pair of photosensitive elements. Relative movement causes the beam to move with respect to the photosensitive elements. The movement of the beam actuates a restorative means which repositions the beam at its initial position. The extent of movement of the restorative means indicates the amount of primary beam movement. The improvement of this invention is an alarm means which assumes a malfunctionindicating condition when the primary beam is extinguished or and when the primary beam is displaced from its initial position by a distance greater than the small excursions of movement experienced during normal operations. In the disclosed embodiment, an alarm-actuating means includes a photosensitive element located in the path of a secondary beam of light which emanates from the same source and moves concurrently with the primary beam.

United States Patent [191 King 1 RELATIVE MOVEMENT SYSTEM HAVING ALARMMEANS [75] Inventor: Paul B. King, Mountain Lakes, NJ.

[73] Assignee: The Cessna Aircraft Company,

Wichita, Kans.

[22] Filed: May 22, 1973 [21] Appl. No.: 362,729

[58] Field of Search 340/27 R, 27 NA, 27 AT; 250/204, 210, 237 R;318/640, 565; 73/178 R, DIG. ll

[56] References Cited UNITED STATES PATENTS 2,731,831 1/1956 Schaefer f.73/178 R 3,590,356 6/1971 Hofmeister 250/204 3,612,881 10/1971 King250/204 3,783,277 1/1974 Younkin et al. 250/204 [l1] 3,867,716 [4 1 Feb.18,1975

Primary Examiner-William C. Cooper Assistant ExaminerRandall P. MyersAttorney, Agent, or FirmBrowne, Beveridge, DeGrandi & Kline [57]ABSTRACT A primary beam of light is directed on a pair of photosensitiveelements. Relative movement causes the beam to move with respect to thephotosensitive elements. The movement of the beam actuates a restorativemeans which repositions the beam at its initial position. The extent ofmovement of the restorative means indicates the amount of primary beammovement. The improvement of this invention is an alarm means whichassumes a malfunction-indicating condition when the primary beam isextinguished or and when the primary beam is displaced from its initialposition by a distance greater than the small excursions of movementexperienced during normal operations. In the disclosed embodiment, analarm-actuating means includes a photosensitive element located in thepath of a secondary beam of light which emanates from the same sourceand moves concurrently with the primary beam;

8 Claims, 1 Drawing Figure 1 RELATIVE MOVEMENT SYSTEM HAVING ALARM MEANSThis invention relates to a malfunction-indicating alarm whichpreferably is used in conjunction with a relative movement detector andsystem of the general type disclosed in my US. Pat. No. 3,612,881.

Relative movement detectors of this type operate on the principle thatrelative movement between a pair of bodies causes the movement of a beamof light with re spect to the faces of two photosensitive elements. Suchmovement causes a change in the relative amount of illumination of thephotosensitive elements and causes an unbalanced condition in a bridgecircuit which creates an error signal. The error signal actuates a servomotor which returns the beam to its initial position with respect to thephotosensitive elements. The extent of movement of the servo motor isindicative of the extent of relative movement between the bodies. In thenormal operation of devices of this type, the beam is returned to itsinitial position by means of the bridge circuit and the servo motorwhich are collectively referred to herein as a restorative means.

The usual type of malfunction-indicating alarm for instrumentation hasinvolved a malfunction-indicating device which is actuated upon failureof the primary power of the system. Such devices utilize anormallyenergized solenoid which holds a malfunctionindicating flag in aconcealed position. When primary power is lost, the solenoid isdeenergized and the ma]- function-indicating flag is moved by a springor other means to a visible position.

According to the present invention, the malfunctioning of the system isindicated not only upon the loss of primary power, but also when thelight beam is displaced significantly from its initial position withrespect to the photosensitive elements; i.e., when the beam moves beyondthe small excursions of movement which are encountered during normaloperations. This condition of malfunction can be caused by failure of avariety of elements of the system, for example when there is a failureof one or both of the photosensitive elements, a failure of thecircuitry which creates the error signal when the photosensitiveelements are not equally illuminated, a failure of the servo motor whichrestores the beam to its initial position, a failure of the beammovingmechanism connected to the servo motor, or a failure of a lamp which isthe source of the beam of light. Further, if the solenoid of themalfunction-indicating alarm is defective, the observer will be alertedto this condition.

According to the invention, the malfunction signalling means is actuatedin response to relative movement between the photosensitive elements andthe primary beam of light. Alarmactuation occurs when this movementexceeds the small excursions of movement which are normally offset ornullified by a properly functioning restorative means.

For a more complete understanding of the invention, reference is made tothe accompanying drawings which show, in diagrammatic form, a systemwhich operates according to the invention.

In the drawings, it will be seen that a primary beam of light is createdby a lamp 2 and a vertically movable baffle 4 which has a transparentarea 6 defining the boundaries of the beam. The beam is directed onto apair of adjacent photosensitive elements 8 and 10. A

beam splitting shield 12 may be used as described in my previous US.Pat. No. 3,612,881, but it is not essential to the practice of thisinvention.

In its initial position, baffle 4 will direct the primary beam of lightin a given ratio, usually one-to-one, onto the photosensitive elements 8and 10. The baffle 4 is mounted on the upper end of a vertically movablesupport rod 14 which is connected to the upper face of an aneroidbellows 16. Changes in the surrounding pressure will cause expansion andcontraction of the aner' oid bellows 16, resulting in vertical movementof the rod 14, the baffle 4 and the light beam established thereby. Inan altimeter system, increases in altitude cause the aneroid bellows 16to expand, raising the baffle 4 and moving the beam relative to thephotosensitive elements. This increases the area of illumination of thephotosensitive element 8 and decreases the amount of illumination of thephotosensitive element 10. These photosensitive elements are connectedelectrically to a motor control circuit 13 which senses any change inthe relative amounts of illumination of the elements 8 and 10. Anunbalanced condition creates an error signal which actuates a servomotor 15 connected to the control circuit 13 by the conductors 17 and18. It will be understood that upward movement of the baffle 4 and theresulting increased illumination of the photosensitive element 8 willcreate an error signal which produces servo movement tending to drivethe baffle 4 downwardly so that the photosensitive elements 8 and 10will again receive a balanced amount of illumination from the primarybeam of light. This downward movement of the baffle is produced bylowering the expanded aneroid bellows 16. The servo motor 15 is providedwith a gear 20 which meshes with the gear 22. An aperture in the centerof gear 22 is internally threaded to receive the threaded lower portionof the nonrotatable bellows-supporting rod 24. Rotation of the gear 22will move the primary light beam as a result of vertical movement of therod 24 and consequent vertical movement of the entire aneroid bellows16, shaft 14 and baffle 4.

In the normal use of apparatus such as described above, the baffle 4 iscontinually being returned to its initial or null position where thetransparent area 6 is positioned to provide the appropriate illuminationto the photosensitive element 8 and 10. Of course, there is somedeparture from this initial position in the time interval before theerror signal is capable of actuating the servo motor. However, theseexcursions from the initial position are relatively small, and theextent of relative movement is, in fact, determined by the extent ofmovement of the rod 24 which is moved to offset the movement produced bythe expansion and contraction of the aneroid bellows 16. The extent ofmovement of the rod 24 may be indicated in a number of ways, one beingshown as a simple gear arrangement 26 for driving the dial indicator ofan altitude-indicating device 30.

According to the preferred and illustrated embodiment of the invention,the malfunction alarm is actuated in response to relative movementbetween the primary light beam and the photosensitive element which isgreater than the small excursions of relative beam movement which areencountered during normal operation of the apparatus. This malfunctionalarm system includes a mirror 32 which is located in the path of lightfrom the illumination lamp 2. The light which strikes the mirror 32 isdirected horizontally through a second transparent area 34 in the baffle4, to establish a secondary beam of light which is directed against amalfunction-sensing photosensitive element 36. During normal operations,the secondary beam of light will strike the photosensitive element 36which, through the alarm control circuitry 38, normally actuates thesolenoid 40. When actuated, the solenoid 40 holds the flag of the alarmsignaling device 42 in a concealed position. However, upon thedeenergization of the solenoid 40, the flag will move to a visibleposition in the window 44 to provide a visible indication that thedevice is not functioning properly.

The relationship between the secondary beam of light and thephotosensitive element 36 is such that the alarm control circuit 38 willbe shifted to a malfunction-indicating condition when the quantum oflight striking the photosensitive element 36 becomes less than athreshhold amount. This occurs upon failure of the light source or uponmovementof the baffle 4 an excessive distance from its initial or nullposition. For example, this will happen when the primary power is lostsince the lamp 2 will be extinguished. It also will occur when the lamp2 becomes burned out. A malfunction will be indicated when there is afailure of either or both of the primary photosensitive elements 8 or 10since this will result in improper repositioning of the baffle by therestorative means. Similarly, defects in the motor control system 13,the electrical servo motor or the mechanisms which are used to raise andlower the aneroid bellows 16 under the influence of the servo motor willresult in an inaccurate repositioning of the bellows. Even when thealarm solenoid 40 fails, the alarm flag will move to themalfunction-indicating position in the window 44.

When the device is used as an altimeter, even a momentary failure toindicate the amount of bellows expansion will be indicated to theobserver. For example, if an aircraft loses altitude at a rapid rate sothat the servo motor cannot operate quickly enough to restore the baffle4 to its null position, the'malfunction device will assume itsmalfunctionindicating condition. When the servo motor catches up so thatthe altimeter reflects the correct altitude, the alarm solenoid 40 willagain be actuated to indicate to the observer that the altitude readingis correct.

Those skilled in the art will readily be able to construct a deviceoperating according to the principles of this invention. Thephotosensitive elements 8 and 10 may be photoemissive, photoresistive,photoconductive elements, the latter type of which may be thehermetically sealed dual element cell of the type CL 705 L/2manufactured by Clairex Corporation of New York, New York. These cellsare of the cadmium sulfide type and the resistance varies from 50,000ohms to 7,500 ohms as the light striking them varies from total darknessto 2 foot candles. The motor control circuit 13 is preferably abalancing circuit of the bridge type which creates an error signal in awell known manner. Similarly, a bridge circuit is suitable for detectingthe non-illumination or reduced illuminationof'the secondary cell 36which is struck by the secondary beam of light. The alarm itself ispreferably of the flag type but the malfunction signalling means maydirect its signal only to some non-human element capable of shifting thesystem automatically to a standby system if desired. The beams may becreated in other ways, and move through other instrumentalities such asmirrors rather than baffles. A single transparent area in a baffle mightbe used to create a beam which serves both as the primaryposition-indicating beam and the secondary alarm-actuating beam. Theratio between the quantities of light striking the photosensitiveelements when the apparatus is at its null or balanced position may varyfrom the 1:1 ratio described above. Some systems may include a means toshift the null position of the baffle 4, but the shifted null positionwill still be within the small permissible excursions of the baffle. Inlieu of or in addition to the indicator device 30, an altimeter sys-.tem may have an altitude-indicating means in the form of anautopilotsystem or a transponder which transmits an altitude indicating radiosignal to a remote station. In view of these and other modifications andvariations to the illustrated system, it is emphasized that theinvention is not limited only to the disclosed embodiment, but isencompassing of a wide variety of systems which fall within the spiritof the following claims.

I claim: 1. In an apparatus for sensing relative movement between a pairof bodies, said apparatus having a pair of photosensitive elements,means for directing a primary beam of light onto both of saidphotosensitive elements, said primary beam having a null position wherethe quantities of light striking said photosensitive elements arebalanced in a given ratio, means for moving the primary beam throughsmall excursions in response to relative movement between said bodies tochange the ratio of light striking the photosensitive elements,restorative means responsive to signals from the photosensitive elementsfor moving the bodies to reestablish the balanced condition where thequantities of light striking the photosensitive element are in saidgiven ratio, an improvement comprising an alarm means for indicatingmalfunction of the apparatus, said alarm means including a malfunctionsignalling means having a normal operational condition and amalfunction-indicating condition, and alarm actuating means for shiftingthe alarm means to its malfunction-indicating condition in response todisplacement of the primary beam beyond a predetermined limit of saidsmall excursions, said alarm actuating means includes a circuit havingan alarm-actuating photosensitive element, means for directing asecondary beam of light on the alarm-actuating photosensitive elementonly when the primary beam of light is at a distance less than saidpredetermined limit of said small excursions from its null position,said means for moving the primary beam also moving the secondary beam. I2. The apparatus of claim 1 wherein said means for directing a primarybeam of light includes an illumination means and a primary baffleinterposed between said illumination means and said pair ofphotosensitive elements, said primary baffle having a light-perviousarea which forms the primary beam, said primary baffle being movable bythe restorative means and the means for directing a secondary beamincludes a baffle portion interposed between said illumination means andthe alarm-actuating photosensitive element, said baffle portion having alight-pervious area for directing the secondary beam on thealarm-actuating photosensitive element only when the primary beam oflight is at a dis tance less than said predetermined limit of said smallexcursions from its null position.

3. The apparatus of claim 2 wherein said primary and secondary bafflesare concurrently movable and are immovable with respect to each other.

4. The apparatus of claim 1 having aneroid bellows means for moving theprimary beam of light whereby the apparatus functions as an altimeter.

5. The apparatus of claim 4 having indicating means for indicating theamount of movement of the restorative means.

6. The apparatus of claim 5 wherein the indicating means provides analtitude input indication to an altitude-indicating transmitter.

7. The apparatus of claim 5 wherein the indicating means provides analtitude input indication to an autopilot system.

8. In a photometric altimeter system having means for directing a lightbeam from a light source onto a pair of photosensitive elements, saidmeans directing said light on said photosensitive elements in apredetermined ratio, altitude responsive means for moving the light beamrelative to said photosensitive elements to change the ratio of lightstriking said photosensitive elements, means responsive to the changedratio for moving the beam of light to reestablish said predeterminedratio, the improvement comprising a malfunction alarm system includingmeans independent of said balanced bridge circuit for producing an alarmsignal, said means for producing an alarm signal being responsive to andactuated by relative movement of the beam beyond a predetermined limit,and means responsive to said alarm signal for indicating an alarmcondition in said photometric altimeter system. l= l

1. In an apparatus for sensing relative movement between a pair ofbodies, said apparatus having a pair of photosensitive elements, meansfor directing a primary beam of light onto both of said photosensitiveelements, said primary beam having a null position where the quantitiesof light striking said photosensitive elements are balanced in a givenratio, means for moving the primary beam through small excursions inresponse to relative movement between said bodies to change the ratio oflight striking the photosensitive elements, restorative means responsiveto signals from the photosensitive elements for moving the bodies toreestablish the balanced condition where the quantities of lightstriking the photosensitive element are in said given ratio, animprovement comprising an alarm means for indicating malfunction of theapparatus, said alarm means including a malfunction signalling meanshaving a normal operational condition and a malfunction-indicatingcondition, and alarm actuating means for shifting the alarm means to itsmalfunction-indicating condition in response to displacement of theprimary beam beyond a predetermined limit of said small excursions, saidalarm actuating means includes a circuit having an alarm-actuatingphotosensitive element, means for directing a secondary beam of light onthe alarmactuating photosensitive element only when the primary beam oflight is at a distance less than said predetermined limit of said smallexcursions from its null position, said means for moving the primarybeam also moving the secondary beam.
 2. The apparatus of claim 1 whereinsaid means for directing a primary beam of light includes anillumination means and a primary baffle interposed between saidillumination means and said pair of photosensitive elements, saidprimary baffle having a light-pervious area which forms the primarybeam, said primary baffle being movable by the restorative means and themeans for directing a secondary beam includes a baffle portioninterposed between said illumination means and the alarm-actuatingphotosensitive element, said baffle portion having a light-pervious areafor directing the secondary beam on the alarm-actuating photosensitiveelement only when the primary beam of light is at a distance less thansaid predetermined limit of said small excursions from its nullposition.
 3. The apparatus of claim 2 wherein said primary and secondarybaffles are concurrently movable and are immovable with respect to eachother.
 4. The apparatus of claim 1 having aneroid bellows means formoving the primary beam of light whereby the apparatus functions as analtimeter.
 5. The apparatus of claim 4 having indicating means forindicating the amount of movement of the restorative means.
 6. Theapparatus of claim 5 wherein the indicating means provides an altitudeinput indication to an altitude-indicating transMitter.
 7. The apparatusof claim 5 wherein the indicating means provides an altitude inputindication to an autopilot system.
 8. In a photometric altimeter systemhaving means for directing a light beam from a light source onto a pairof photosensitive elements, said means directing said light on saidphotosensitive elements in a predetermined ratio, altitude responsivemeans for moving the light beam relative to said photosensitive elementsto change the ratio of light striking said photosensitive elements,means responsive to the changed ratio for moving the beam of light toreestablish said predetermined ratio, the improvement comprising amalfunction alarm system including means independent of said balancedbridge circuit for producing an alarm signal, said means for producingan alarm signal being responsive to and actuated by relative movement ofthe beam beyond a predetermined limit, and means responsive to saidalarm signal for indicating an alarm condition in said photometricaltimeter system.